1. Field of the Invention
The present invention relates to a switchback device, provided in a conveyance path for a printed medium, for reversing the direction of movement of the medium and then delivering the medium from an upstream part to a downstream part of the conveyance path.
2. Description of the Related Art
In an inkjet printer, a photo printing/developing machine, or the like, a printed medium such as a printed paper is discharged from the machine preferably in a state wherein the printed face of the medium faces upward, in order that the user can easily check the printed condition. For this purpose, some such machines are provided with switchback devices in their media conveyance paths.
JP-A-2001-142190 discloses a photo printing/developing machine including a switchback device. As shown in FIGS. 7 and 8, the switchback device 102 is provided between an upstream part 100 of a conveyance path and a downstream part 101 of the conveyance path. The switchback device 102 includes a pair of operation rollers 105 including a drive roller 103 and a slave roller 104; plate-like fixed guides 107 for guiding a medium 108 along both faces of the medium 108 from a pair of rollers 106 in the upstream part 100 of the conveyance path to the pair of operation rollers 105; and a rotatable switchback guide 109 for changing the direction of the medium 108 being pinched by the pair of operation rollers 105, and then guiding the medium 108 to the downstream part 101 of the conveyance path. The switchback guide 109 does not rotate relative to the medium 108.
FIG. 7 is a side view showing a state wherein the medium 108 is being taken in the switchback device 102. The medium 108 being conveyed from the pair of rollers 106 in the upstream part 100 of the conveyance path is guided to the pair of operation rollers 105 by the fixed guides 107. The medium 108 comes into contact with the switchback guide 109 and the direction of the movement of the medium 108 is changed downward at a nearly right angle by the switchback guide 109. The medium 108 is then pinched by the pair of operation rollers 105. In this process, the leading edge and the printed face 108a of the medium 108 come into contact with the switchback guide 109 and they are rubbed by the switchback guide 109.
FIG. 8 is a side view showing a state wherein the medium 108 has been completely taken in the switchback device 102. When the rear end portion of the medium 108 is pinched by the pair of operation rollers 105, the switchback guide 109 rotates by its own weight in the direction indicated by an arrow in FIG. 8. The pair of operation rollers 105 is then reversed in rotation. Because the switchback guide 109 has rotated, the medium 108 is guided by the switchback guide 109 to a pair of rollers 110 in the downstream part 101 of the conveyance path, as shown by an alternate long and two short dashes line in FIG. 8. Thus, the medium 108 is, after switchback, guided to the downstream part 101 of the conveyance path.
JP-A-2001-142190 further discloses another switchback device in which the slave roller 104 is disposed at a position somewhat lower than the drive roller 103 and the switched guide 109 is fixed.
In JP-A-2001-142190, the printed face 108a of the medium 108 comes into contact with the switchback guide 109, which does not rotate relative to the medium 108. In this state, the medium 108 is forcibly bent and guided by the switchback guide 109. This may cause scratches and dirt on the printed face 108a. In addition, because one fixed guide 107 is provided between the pair of rollers 106 in the upstream part 100 of the conveyance path and the pair of operation rollers 105 so as to face the printed face 108a of the medium 108, the fixed guide 107 may cause scratches and dirt on the printed face 108a if the medium 108 is curved.
Further, the drive roller 103 can not be reversed until the rear end portion of the medium 108 is pinched by the pair of operation rollers 105. Thus, a large space is required so that the whole medium 108 can be taken in for switchback. This makes it difficult to reduce the size of the device.